Boot loader

Package/package repository format

Add support for repository keys (public/private) and package signing/check sums, so that it is possible to verify that data retrieved from a repository have not been tampered with.

Add package sizes to repository. Since there are plans to support xz (or other high-ratio formats) compressed uncompressed packages for download that are recompressed for installation, we probably need to discriminate between download and installation sizes.

Add support for a faster compression format (e.g. ​lz4). As it turns out, the currently used zlib compression is rather slow (slower than reading uncompressed data from a slow HD).